ARTICLES FROM A POLYESTER RESIN REINFORCED WITH GLASS FIBRE

Abstract: Articles from a polyester resin reinforced with glass fibre obtained by melt-shaping of the resin mixed with the glass fibre and a polyfunctional compound capable of increasing the intrinsic viscosity of the resin by addition reactions with the end groups of the resin using melt residence times during the shaping phase lower than 120 sec. and temperatures lower than 300 DEG C.

Description: Articles from a polyester resin reinforced with glass fibre The present invention relates a process for the prepara¬ tion of glass fibre articles reinforced from polyester resin. It is known that the addition of glass fibre to the polyester resin may improve the mechanical properties of the resins and particularly their impact strength. It is known from USP 3,553, 157 the production of articles with thick walls by shaping the resin in the molten state carried out in the presence of polyfunctional compounds capable to react with the resin end groups and to lead to the extension of the polymer chain in order to counterba¬ lance the thermal degradation reactions which occur during the shaping process of the article. It is possible to obtain shaped articles with sufficiently high values of intrinsic viscosity to ensure the necessary mechanical properties to the article. In the USP patents 3,553,157 are described also the rein¬ forcement with lass fibres of the shaped articles. The fibres are preferably used in a quantity comprised between about 10 and 45% by weight. The polyfunctional compounds most preferred are the poly- isocyanates. It is also described the use of tetracaboxyi1ic acid dianhydrides and particularly the use of the pyromel- litic anhydride (PMDA). As already indicated, the presence of polyfunctional compounds during the shaping phase allows to obtain shaped articles with intrinsic viscosity higher than that of the starting polymer, and which, in the case of the polyisocya- nates, can arrive to 3dl/g or more. Regarding the use of PMDA the I.V. highest value is about 0.84 dl/g. The I.V. increase depends from the PMDA concentration; it reaches a peak and than decreases. The highest theoretical value of the increase is obtained when the PMDA concentration corresponds to that necessary to react with all the reactive groups of the resin. The viscosity decreases when PMDA is in an excess of said value. Regarding the shaping of articles reinforced with glass fibres it has been observed that the polymer intrinsic viscosity decreases considerably with respect to the value obtainable in the shaped articles, not reinforced with glass fibres. The above situation practically excludes the possibility to obtain articles reinforced with glass fibres having I.V. values sufficiently high to show the good mechanical properties obtainable with high values of I.V. It has been unexpectedly found, and this is in contrast with the teaching deriving from the patent USP 3,553,157, that it is possible to obtain by melt shaping of polyester resins articles reinforced with glass fibres having suffi¬ ciently high values of I.V. to give to the shaped article mechanical properties of high interest. The melt-shaping process of the invention is carried out by shaping the article, in the presence of a polyfunctional compound capable to increase the intrinsic viscosity of the polyester resin by addition reactions with the resin end groups, using residence times during the melt-shaping lower than about 120 sec. preferably comprised between 20 and 100 sec. and temperatures of the molten resin lower than about 300°C preferably comprised between 260 and 280°C. The residence time generally decreases with the tempera¬ ture increase. The polymer intrinsic viscosity in the shaped article is higher than about 0,6 dl/g and is preferably comprised between 0,7 and 1,8 dl/g. In conformity with the preferred mode the resin and the polyfunctional compound are blended in the molten state at a temperatures lower than 300°C and with residence times lower than 200 sec. preferably comprised between 20 and 100 sec. The obtained chips are fed to a co-rotating twin screw extruder; the glass fibres are then fed and blended with the molten polymer and the mixture is extruded to shape the article. The residence time of the mixture blended with the glass fibres is lower than about 120 sec. The shaped article can be subjected to a solid state poly- addition treatment carried out at a temperature between 180 and 200°C to obtain an additional increase of polymer intrinsic viscosity and also a higher dimensional stability to the thermal deformation. The I.V. after the upgrading treatment can attain values higher than 1.0 dl/g. The cooling of the shaped article can be carried out slowly and in a controlled way to allow the polymer crystal¬ lization without using thermal treatments, which are gene¬ rally carried out at temperatures higher than 100° prefe¬ rably comprised between 140 and 170°C. The crystallization brings about improvements of the mechanical properties such as the flexional strength, but it tends to reduce the impact strength. The polyfunctional compound is preferably selected from the dianhydrides of the aromatic tetracarboxylic acids. The pyromellitic dianhydride is the preferred compound. Other dianhydrides usable are those of 3 , 3 ' 4,4' dipheniltetracar- boxylic acid, (perilene 3, 4, 9, 10) tetracarboxylic acid, 3,3' 4,4' - benzophenonetetracarboxylic aci ' d 2,2 - bis(3,4- dicarboxyphenyl ) propane, bis (3,4 - dicarboxyphenyl ) ether, bis (3,4 dicarboxyphenol ) sulfone 1, 2, 3, 4 cyclobutane- tetracarboxylic acid 2, 3, 4, 5 tetracarboxyhydrofuran. The polyfunctional compounds are used in a quantity from about 0.05 to 2% by weight on the resin. The addition of the glass fibres increases considerably the impact strength, the flexional modulus and the stress at break of the shaped articles. The use of quantities of about 5% by weight has already the effect to improve the mechanical properties; the preferred concentration of glass fibres are generally comprised between 10 and 50% by weight. The glass fibres have generally a length from 0,2 to 1 mm. The finishing agents are of known type and can include compounds such as vinyltrichlorosilane Cr-methacrylates and of other metals, titanium alcoholates. Conventional additives can be added to the resin such as stabilizers, antioxidants, plasticizers, nucleating com¬ pounds, pigments, flame retardant compounds, inert reinforc¬ ing charges, such as calcium carbonate, talc. The glass reinforced resins usable in the process of the invention, due to their melt-rheological properties charac¬ terized by high shear sensitivity are particularly suitable for foaming end extrusion blow-moulding applications. The polyester resins used in the invention process are the product of the polycondensation reaction of an aromatic dicarboxylic acid such as terephthalic acid or its derivati¬ ves such as dimethylester or naphthalendicarboxylic acids with dyols with 2-12 carbon atoms such as ethylene glycol, 1.4-cyclohexanglycol , 1.4-butandyol . In the definition are also comprised copolymers in which part of the units deriving from the terephthalic acid (up to about 25%) are replaced from isophthalic acid other from other dicarboxylic acids. The polyethylenterephthalate and naphthalenates are the preferred resins. The polyester resin can be mixed with other compatible polymers such as polycarbonates, polycaprolactone in amounts up to about 20% by weight. The addition of small amounts up to 5% by weight of polymers or compounds having properties of liquid crystals and containing reactive groups such as the OH and NH 2 groups improves the mechanical properties. EXAMPLE 1 30 Kg/h of polyethylenterephthalate (PET) having a melting point at 253°C and intrinsic viscosity of 0.66 dl/g are continuously fed from the melt-polycondensation section of PET, to a counter rotating not intermesching twin screw extruder with 30 mm diameter and with outgassing device 590 g/h of a mixture of 20% by weight of pyromellitic dianhydri- de (PMDA) of crystalline PET (I.V. = 0.64 are continuously fed to the extruder by using a gravimetric dosing device. The test conditions were as follows: - pyromellitic dianhydride in the melt = 0.6% by weight - screw speed = 415 RPM - screw ratio length (L/D) = 24 - Average residence time = 18-25 sec - barrel temperature = 283°C - melt temperature = 290 β C A die with double hole is used for the extrusion (dia. = 7 mm) . A strand pelletizer is used to obtain cylindrical chips with 3 mm dia. and 55 mm length. The chips intrinsic viscosity is 0.65 dl/g. 10 Kg/h of so obtained chips are fed after drying to a twin screw extruder with dia. 70 mm and ratio L/D 32. After polymer melting (L/D = 12) the established glass fibre amount is fed through a lateral door. The remaining length (20 L/D) is used for mixing the glass fibres with the polymer. The residence time in the extruder is of 60-90 sec. The mixture is extruded through a flat die of 750 mm length and collected on 3 cooled drums and then further cooled to stabilize the obtained foil. A part of a foil is subjected to upgrading at 190 β C for 12 hours. The mechanical properties are shown in the table where are also reported the mechanical properties of the roil not subjected to upgrading. The mechanical properties were determined with a Histron Series 4500 machine operating at 10 mm/min and at room temperature. At least 5 specimens for each sample were tested. The impact properties were determined by using a Tester Izod Ceast using a 2J hammer and notched specimens. TABLE FOILS Intrinsic Tensile IZOD iβpact Viscosity dl/g Hodulus 8>a strength J/ι (*) The highest values were referred to the extrusion direction, the lowest ones to an orthogonal direction. EXAMPLE 2 Results similar to those reported in example 1 were obtained using PET scraps having I.V. = 0.62 dl/g and melting point of 253°C instead of the example 1.

Claims: CLAIMS 1. Process for the preparation of glass fibres reinforced articles from a polyester resin comprising melt-shaping the resin mixed with glass fibres and a polyfunctional compound capable of increasing the intrinsic viscosity of the polymer by addition reaction with the resin end groups, using residence times during the melt-shaping lower than 120 sec. and with temperatures of the molten phase lower than 300°C. 2. Process according to claim 1 where the glass fibre is used in a quantity between 10 and 50% by weight. 3. Process according to claims 1 and 2 where the polyfun¬ ctional compound is the pyromellitic anhydride used in a quantity from 0.05 to 2% by weight on the resin. 4. Articles in polyester resin reinforced with glass fibres having intrinsic viscosity higher than 0.6 dl/g. 5. Foamed articles from glass reinforced polyester resins having intrinsic viscosity higher than 0.06 dl/g.

Inventors: AL GHATTA HUSSAIN ALI KASHIF, COBROR SANDRO, SEVERINI TONINO, AL GHATTA, HUSSAIN, ALI, KASHIF, COBROR, SANDRO, SEVERINI, TONINO
Applicants: AL GHATTA HUSSAIN ALI KASHIF, COBROR SANDRO, M & G RICERCHE SPA, SEVERINI TONINO, AL GHATTA, HUSSAIN, ALI, KASHIF, COBROR, SANDRO, M.& G. RICERCHE S.P.A, SEVERINI, TONINO
Application year: 1994
Main classification: C08K7
IPC codes: B29C47, B29C55, B29C71, B29K67, C08G63, C08J3, C08J5, C08J7, C08K5, C08K7, C08L67